Commercial processes for the production of organic fluorides have been based on the halogen exchange of an organic chloride with arsenic trifluoride as illustrated by the following general equation: EQU 3RCl+ AsF.sub.3 .fwdarw. 3RF+ AsCl.sub.3
(R being an organic moiety)
The organic fluoride is usually purified by standard procedures such as extraction or distillation. Such process may require the removal and storage of the arsenic trichloride.
As is evident from the above reaction scheme, arsenic trichloride is generated in an amount proportional to the amount of arsenic trifluoride consumed. However, arsenic trichloride has limited resale value, and disposal presents a costly and time-consuming process. Consequently, it is desirable to utilize arsenic trichloride as a starting material in any economical process for producing arsenic trifluoride based upon the aforesaid reaction.
Conventional procedures for manufacturing arsenic trifluoride usually employ either arsenic trioxide or arsenic trichloride as starting materials, and may or may not include a catalysis agent.
For example, arsenic trioxide, (As.sub.2 O.sub.3), may be reacted with a fluorinating agent, such as hydrogen fluoride, (HF), to produce arsenic trifluoride, (AsF.sub.3). EQU as.sub.2 O.sub.3 + 6HF.fwdarw. 2AsF.sub.3 + 3H.sub.2 O
calcium fluoride, (CaF.sub.2), and concentrated sulfuric acid, (H.sub.2 SO.sub.4), may also be used as starting materials with a similar effect: EQU 3CaF.sub.2 + 3H.sub.2 SO.sub.4 .fwdarw. 6HF+ 3CaSO.sub.4 EQU as.sub.2 O.sub.3 + 6HF.fwdarw. 2 AsF.sub.3 + 3H.sub.2 O
both of these methods are accompanied by several economic and time-consuming disadvantages: extensive distillation of reaction products is required to purify the arsenic trifluoride; hydrogen fluoride, a highly corrosive substance, requires special equipment and handling procedures; and hydrogen fluoride, with a low boiling point of 19.5 degrees Centigrade, must be shipped and stored in pressure-tested vessels.
In addition, hydrogen fluoride gas is highly toxic by ingestion and inhalation, as well as strongly irritant to the eyes, skin and mucous membranes, and therefore represents a constant industrial health and safety hazard.
Another process reacts arsenic trichloride, (AsCl.sub.3), with ammonium fluoride, (NH.sub.4 F), in the presence of liquid sulfur dioxide, (SO.sub.2), to generate arsenic trifluoride: ##STR1##
A disadvantage of this method is the required presence of sulfur dioxide, a highly toxic and irritating substance.